A comprehensive understanding of the control of amniotic fluid volume is of major clinical importance and has prompted much research into the mechanism of its regulation. The present application proposes to elucidate the role of vascular endothelial growth factor (VEGF) in promoting angiogenesis and permeability of amniotic, chorionic and cotyledonary blood vessels and examine its role in regulation of amniotic fluid volume and composition. Using the pregnant sheep as the animal model, and combining molecular with physiological approaches, five specific aims are proposed. Aim 1 will characterize the tissue distribution and abundance of VEGF protein and mRNA in fetal amnion, chorion and placental cotyledons by immunohistochemistry, immunoassay, in situ hybridization, Northern blot analysis and competitive RT-PCR. The hypothesis is that VEGF expression is present in cells adjacent to the amniotic, chorionic and placental blood vessels at levels higher than that in other cell types. Aim 2 will determine the cellular distribution and expression of VEGF receptor mRNA in fetal membranes and placenta. The hypothesis is that VEGF receptors are expressed in vascular endothelial cells of these tissues. Aim 3 will investigate the regulation of VEGF gene expression in fetal membranes and placenta by hypoxia and fetal esophageal ligation. The hypothesis is that fetal hypoxia or esophageal occlusion induces VEGF gene expression. Aim 4 will determine the biological function of VEGF in fetal membranes and placenta. Vascular angiogenesis will be evaluated by morphometric analysis, and vascular permeability estimated by permeability to radioactive albumin, sodium and urea. The hypothesis is that VEGF has both angiogenic and permeability properties in these tissues. Aim 5 will utilize a transgenic mouse model carrying a dominant-negative mutant of the VEGF receptor which renders the receptor ineffective. The hypothesis is that the lack of a functional VEGF receptor results in abnormal amniotic fluid volume and composition during pregnancy due to reduction in microvessel density and permeability in the membranes. The proposed studies will provide important information on the regulation of the microvascular network which perfuses the fetal membranes and fetal surface of the placenta. This information will significantly improve the understanding of amniotic fluid volume regulation during pregnancy.